1. Field of the Invention
The present invention relates to a charge-pump type switching power supply apparatus.
2. Description of the Related Art
For the compact-size information terminals in recent years such as mobile phones and PDAs (Personal Digital Assistance), there are some devices such as LEDs (Light Emitting Diode) used for the backlight of a liquid display, for instance, wherein they require a voltage higher than the output voltage of a battery. For example, Li-ion batteries are often used for these small-size information terminals. The output voltage thereof is normally about 3.5 V, and when fully charged, it is about 4.2 V. However, as the LED driving voltage, the LED requires voltage higher than the battery voltage. Accordingly, when the voltage higher than the battery voltage is required, a booster circuit of a switched-capacitor or the like method is used to boost the battery voltage so as to obtain the voltage necessary for driving a load circuit such as an LED. There are cases where a negative power supply is required by such a small information terminal device. In such a case, too, a voltage inverter circuit of a charge-pump method is used to obtain a desired negative voltage (See Reference (1) in the following Related Art List, for instance).
Related Art List    (1) Japanese Patent Application Laid-Open No. 2001-258241.    (2) Japanese Patent Application Laid-Open No. 2005-224060.    (3) Japanese Patent Application Laid-Open No. 2005-224059.
Consider a case where in a small information terminal device both a load circuit requiring voltage higher than the battery voltage and a load circuit requiring negative voltage are driven simultaneously. In such a case, a method is conceivable where a booster circuit and a voltage inverter circuit for supplying voltage to the respective load circuits are mounted respectively. In this method, however, a flying capacitor must be provided each for the booster circuit and the voltage inverter circuit. The capacitance of a flying capacitor is large in general and therefore the flying capacitors are often provided as external circuit components (chip components). Thus, if this external flying capacitor is provided for each power supply apparatus, the number of circuit components will increase, which in turn obstructs a demand for reduction in size and cost of small information terminals.